Using the Firebase Console, add an Android app to your project:
Follow the assistant, download the generated google-services.json file and place it inside android/app. Next,
modify the android/build.gradle file and the android/app/build.gradle file to add the Google services plugin
as described by the Firebase assistant. Ensure that your android/build.gradle file contains the
maven.google.com as described here.

Using the Firebase Console, add an iOS app to your project:
Follow the assistant, download the generated GoogleService-Info.plist file, open ios/Runner.xcworkspace
with Xcode, and within Xcode place the file inside ios/Runner. Don't follow the steps named
"Add Firebase SDK" and "Add initialization code" in the Firebase assistant.

Breaking change. Fixed CollectionReference.parent to correctly return a DocumentReference.
If you were using the method previously to obtain the parent
document's id via collectionReference.parent().id,
you will have to use collectionReference.parent().documentID now.

Breaking change. Migrate from the deprecated original Android Support
Library to AndroidX. This shouldn't result in any functional changes, but it
requires any Android apps using this plugin to also
migrate if they're
using the original support library.

Breaking change. Upgraded to Gradle 4.1 and Android Studio Gradle plugin
3.0.1. Older Flutter projects need to upgrade their Gradle setup as well in
order to use this version of the plugin. Instructions can be found
here.